package utils;

import java.text.NumberFormat;

/**
 * Created by aceyin on 15/7/7.
 * 地理位置工具类
 */
public final class GeoUtil {
    /**
     * 地球半径,单位：KM
     */
    private static final double EARTH_RADIUS = 6378.137;

    /**
     * 计算两个经纬度之间的直线距离，单位KM
     *
     * @param lat1
     * @param lng1
     * @param lat2
     * @param lng2
     * @return
     */
    public static double distance(double lat1, double lng1, double lat2, double lng2) {
        double radLat1 = rad(lat1);
        double radLat2 = rad(lat2);
        double a = radLat1 - radLat2;
        double b = rad(lng1) - rad(lng2);
        double s = 2 * Math.asin(Math.sqrt(Math.pow(Math.sin(a / 2), 2) +
                Math.cos(radLat1) * Math.cos(radLat2) * Math.pow(Math.sin(b / 2), 2)));
        s = s * EARTH_RADIUS;
        return format(s);
    }

    private static double format(double s) {
        NumberFormat format = NumberFormat.getInstance();
        format.setMinimumFractionDigits(2);
        format.setMaximumFractionDigits(2);
        return Double.valueOf(format.format(s));
    }

    private static double rad(double d) {
        return d * Math.PI / 180.0;
    }
}
